Oviposition Site Selection and Habitat Characterization of Anopheles Mosquito in Abraka, Delta State, Nigeria

Background: Malaria still remains a life-threatening disease worldwide causing between 190 and 311 million cases of malaria in 2008. Due to the ever increasing resistance to malaria drugs, source reduction has been recognized as a complementary approach to further reduce malaria transmission. Given that the availability of suitable habitats for the oviposition of anopheline mosquitoes increases their breeding and possibly malaria transmission. We proposed that characterizing the breeding site of Anopheles is of major importance for the transition from malaria control to elimination in our study area. However, information on the oviposition sites, characteristics and influencing factors of breeding sites of Anopheles mosquitoes is lacking. This study aimed to determine the preferential oviposition sites, breeding site characteristics and related environmental parameters.
Methods: A study was undertaken in Abraka, Delta State to determine the preferential oviposition sites of Anopheles mosquito and characterize such sites. Potential larval habitats that might harbor anopheline immatures were sampled between August and September. The larval sampling was done by the standard dipping method. The habitats were characterized based on substrate type, turbidity, habitat type, algal coverage, canopy coverage, surrounding vegetation, surface debris and distance to the nearest house. A two way analysis of variance (ANOVA) was employed to test for significant difference in the occurrence of anopheline and culicine larvae in the different aquatic habitats sampled. Correlation analysis was used to assess the relationship between the environmental variables and the occurrence of the anopheline larvae in the habitats sampled and also to assess the relationship among the environmental variables examined.
Results: A total of 80 aquatic habitats in 8 sites were sampled and 1117 anopheline and 370 culicine larvae were collected. Microscopic identification of the adult Anopheles mosquitoes yielded only Anopheles gambiae. There was no significant difference (P>0.05) in the occurrence of anopheline and culicine larvae in the different habitats sampled, but there was significant difference (P<0.05) for habitat type distribution for anophelines only and culicines only. Correlation analysis revealed that the occurrence of anopheline larvae was correlated with some of the environmental variables examined.
Conclusion: The results obtained indicate that Anopheles gambiae prefers open, sunlit and undisturbed habitats for oviposition and that abiotic factors play a vital role in larvae’s habitat preference. Thus such factors should be considered when designing an integrated vector control programs.